Abstract: Background: The Ottawa Subarachnoid Haemorrhage (SAH) Rule is a clinical decision tool to facilitate identification of subarachnoid haemorrhage in neurologically intact adults admitted to the Emergency Department (ED) with acute non-traumatic headache. It had been originally purported that the tool had the potential to reduce neuroimaging rates by approximately 10-20%. We aimed to systematically review the existing literature to examine the validity and usefulness of the rule.

Methods: Medline was searched up to April 2018 using a defined search strategy. No limits were applied. Conference abstracts and articles pertaining to the derivation of the rule were excluded.

Results: 66 unique citations were identified from which 4 articles were deemed to be sufficient quality. Across a total of 3317 patients enrolled from four countries, the Ottawa SAH rule had a pooled sensitivity of 100%. However, its specificity has been shown to be universally poor, with point estimates ranging from 7.6% to 13.6%. The actual or potential reduction in investigation rate has been shown to be relatively modest at 4.7% by two studies. Furthermore, one study suggested that the rule can only be applied to a small proportion (9%) of the ED cohort.

Discussion: Based on the current literature, the Ottawa SAH rule is a reliable clinical decision tool in excluding SAH and can avoid unnecessary investigations in a small, select proportion of patients. It is limited by a poor specificity and clinical judgement must be applied in managing patients who demonstrate one or more high risk features from the rule.Summary: Can the Ottawa Subarachnoid Haemorrhage Rule help reduce neuroimaging rates for suspected subarachnoid haemorrhage? A systematic review.References: 1. Bellolio MF et al. (2015) External validation of the Ottawa subarachnoid hemorrhage clinical decision rule in patients with acute headache. Am J Emerg2. Kimura A et al. New clinical decision rule to exclude subarachnoid haemorrhage for acute headache: a prospective multicentre observational study. BMJ Open3. Perry JJ et al. (2017) Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. CMAJ.4. Chu et al. (2017) Applying the Ottawa subarachnoid haemorrhage rule on a cohort of emergency department patients with headache. Eur J Emerg Med Report abuse »